Topics

1

General Questions and Answers / About the convergence of transmissionspectrum calculation

« on: April 10, 2018, 09:52 »

Dear experts,

I want to calculate the transmission spectrum (or IV curve) of a 2D-device using DFT-GGA method. First of all, I made a k-point scan for kB (periodic along B direction) from 9 to 19 with kA=1 and kC=150. I got the kB dependency of the transmission current, seen in the attached file.
I want to know, what kind of conclusion can I get from the figure, kB=9 is almost sufficient, or kB=19 is still not sufficient?

I appreciate you for your kind help!

2

General Questions and Answers / Can anybody help me with the concept "contributions" in tranmissionpathway?

« on: March 14, 2018, 06:48 »

Dear experts,

I am not sure of the meaning of this sentence " The transmission pathways contributions from the left or right electrode" when I tried to calculate the transmissionpathway of a two-probe device under a certain bias.

What's the difference: contribution from left or right electrode?

Please see the attached picture. It's the transmission pathway of a in-plane hetero-junction. I don't know what's the thickness of the lines stands for.

Does  the thickness of the transmission lines stand for the magnitude of the current flow? But according to my knowledge, the current flow from one electrode to another electrode should be the same along the transport direction. I don't know why there is no transmission lines near the right electrode.

Any other explanations to the question? I forgot if I used the default setting of the transmissionpathway (contribution from left). Do I need to recalculate the transmissionpathway with "contribution from right electrode"?

I appreciate your kind help!

3

General Questions and Answers / Looking for a tutorial about the Bi2Se3 thin film device

« on: March 5, 2018, 14:24 »

Dear ATK staff,

I once saw a tutorial about the topological insulator Bi2Se3 thin film device on the quantumwise website. But now I cannot find it. Can you tell me where I can get to that tutorial? Also, I want to find an older version of the tutorial "mobility".

Best regards,
lknife

4

General Questions and Answers / About the repeatability and correctness of the calculation using ATK

« on: December 22, 2017, 16:09 »

Dear ATK experts,

I am studying the transport properties (transmission spectrum) of a device using Huckel method. I have done two calculations with the same device configuration, the same bias voltage, while there are a little bit differences between the parameters for the calculations, such as k-point sampling, Poison solver, damping factor and so on. Both the two calculations were converged to the same tolerance. Attached are the .py file for the two calculations.

However, the transmission spectrums are quite different. The current in one calculation is about ten times of that in another calculation.

Who can tell me which one is correct and what’s wrong with the other calculation? How should I choose the parameters for the next calculation?

Thank you very much for your kind help!

5

General Questions and Answers / About the convergence of the transmission spectrum calculation

« on: December 19, 2017, 10:38 »

Dear experts,

When calculating the IV curve of a device (I am using the ATK2015 and ATK2016, Huckel method), if I used the "IVCurve" block directly, sometimes it was found that the transmission spectrum did not converge at some specific bias values. Thus, I had to modify manually the parameters of the calculation, such as the damping factor, the history step and the Poison solver, and redo the transmission spectrum calculation bias by bias, which is very inconvenient. In some cases, it was very hard to converge (>1000 iteration steps). However, when changing to a suitable parameter set, it converged within 50-100 steps.

The are two questions about this problem:
(1) Is there any problem if the points of the IV curve were obtained using different parameters?
(2) Is there a better IVCurve block that can adjust the parameters automatically when it's hard to converge?

Thanks a lot for your kind help!

6

General Questions and Answers / how to read the result calculated using newer version ATK?

« on: December 1, 2017, 08:22 »

Dear experts,

I have a permanent license of ATK2015 and temporary license of ATK 2016. I did some simulation with ATK2016 but it now expired and the renew of it is on the way. Now, I wanted to read directly some of the results calculated before using ATK2016, such as transmission spectrum, with ATK2015 but failed. Since I don't want to redo the simulation with ATK2015, can anybody here help me with this problem?

Thank you very much for your kind help!

7

General Questions and Answers / too hard to converge when calculating the transmission spectrum

« on: November 15, 2017, 03:16 »

Dear all,

I am calculating the transmission spectrum of a device bias by bias to get the IV curve. The method I am using is Extended Huckel method and I am using ATK 2015.1. I met several problems about the convergence of the calculation.

Firstly, I have to change some parameters when the bias voltage changes, such as k-point sampling, damping factor and history step, to make the calculation converge. I am not sure if these adjustments will have some influence on the current value calculated.

Secondly, I have big problem about the convergence of one of the calculation. The transmission spectrum calculation converged easily at bias -0.21V, but it cannot converge at bias -0.24V. I have done almost all I can do trying to make it converge.
These attempts include:
1. increasing the k-point sampling from (1,9,100) to (1, 15, 150), even to (1, 20, 200);
2. adjusting the damping factor and history steps with (0.05, 25), (1, 20)(default), (0.3, 12);
3. using the converged configuration under bias -0.21 as the initial state;
4. increasing the maximum iteration steps up to 1500

All of the above attempts were failed. Attached is the .py file for one of the failed calculation. Since the .log file is very large, I cannot post it here.

Thirdly, I heard from the turotial/Forum that I can increase the electron temperature which may be help to the convergece. But I am still not sure if it is all right if the IV curve contains current calculated at different electron temperture.

Can anybody here help me with these problems? Thank you very much for your kind help!

8

General Questions and Answers / cannot install ATK2017.2

« on: November 4, 2017, 16:30 »

Dear experts,

I downloaded ATK2017.2 from the quantumvise website. However, when I tried to install it, there is no sign for the installation. In addition, the source package downloaded from the website was self-deleted. I tried several times and the same phenomenon appeared.

Can anybody here tell me what's the problem with the installation?

Thank you very much for you kind help!

9

General Questions and Answers / What's the definition of bias voltage?

« on: October 18, 2017, 11:28 »

Hi, everyone,

When I calculate the IV curve, what's the definition of the bias voltage, V_R-V_L or V_L-V_R? Here V_R and V_L represent the chemical potential of the right electrode and the left electrode, respectively.

Thank you very much for your attention!

10

General Questions and Answers / asking for the explanation of the IV curve

« on: October 12, 2017, 16:00 »

Dear experts,

I am now studying the tutorial "Transport calculations with ATK", https://docs.quantumwise.com/tutorials/atk_transport_calculations/atk_transport_calculations.html.

I have a question about the IV curve in this tutorial: is there any explanation for the fluctuation of the dI/dV curve or the increased R at bias about 0.9V for this particular device, seen in the attached figure?  Where can I find such explanation from literature?

Thank you very much for your kind help!

11

General Questions and Answers / Is this EDP curve correct?

« on: October 8, 2017, 04:28 »

Hello,

I made a device configuration and calculated the EDP curve of it. However, there is something I cannot understand. Please see the attached figure of the EDP plot and the .py file for it, notifying the Y value of the plot. Can anybody here tell me if the EDP curve is correct? I used the ATK 2016.4 to do the calculation.

Thank you very much for your help!

12

General Questions and Answers / Can ATK simulate superconductivity?

« on: September 13, 2017, 14:14 »

Hi, experts,

I want to know, if ATK can simulate superconductivity? In other words, can ATK deal with the influence of environmental temperature (not the electron temperature) on the conductance of a material? If so, how to do the simulation? If not, can any other simulation package such as VASP or MS do?

Thank you very much for your kind help!

13

General Questions and Answers / Are these EDP curves correct?

« on: September 10, 2017, 15:39 »

Hi, experts,

I got an interface-based device and I wanted to check the length of the device by plotting the ElectrostaticDifferencePotential (EDP) curve of this device. I got two EDP curves, one was for the original device and the other was for the device with doping.  However, the EDP for the doped device is far from an ordinary one, I think. Please see the attached pictures and the python file for EDP calculation.

I want to know: if there is something wrong with the EDP curves, what made the EDP curve for the doped device look like this ?

Thanks very much for your kind help!
 

14

General Questions and Answers / supercell from hexagonal to simple orthorhombic: a problem

« on: September 2, 2017, 03:44 »

Dear experts,

I want to make a supercell from hexagonal unit cell to simple orthorhombic supercell. However, after transforming the lattice, some atoms are not on the expected position, please see the attached files, although it might also OK for the calculation. I want to know how to make the supercell with all the atoms bonded?

Thank you very much for your kind help!

15

General Questions and Answers / How to make full use of my computer?

« on: August 1, 2017, 04:17 »

Dear experts,

Now I got a computer with the CPU model of E5-2620 2.00G (2 processors) and 32G memory. Each CPU has 8 cores. I want to run ATK on this computer.

I have the MPI license installed on another computer cluster for ATK2015. Also, I have the licence for ATK 2016 (teaching licence, working by connecting to the license server, will be renewed to ATK2017 later) to run ATK on local computer. Since the teaching licence does not support the MPI calculation on local computer, I want to know  if it possible to make full use of my computer with 2 processors by threading? (the settings in Job manager for threading seems only support single processor)

Hope anyone here can help me with this question. Thank you very much for your time and kind help!